1. Field of the Invention
The present invention relates to a control system for switching a running state between a two-wheel-drive running state and a four-wheel-drive running state in a four-wheel-drive vehicle that includes a connection-disconnection mechanism disposed closer to a driving power source than a driving power transmission shaft and right and left clutches disposed in power transmission paths to right and left wheels as secondary drive wheels.
2. Description of Related Art
A four-wheel-drive vehicle is well known which includes a connection-disconnection mechanism disposed on a driving power source side of a driving power transmission shaft (for example, propeller shaft) that transmits dynamic power to secondary drive wheels, which serve as driven wheels at the time of two-wheel-drive running (2WD running), at the time of four-wheel-drive running (4WD running) and right and left clutches disposed in power transmission paths to the right and left wheels of the secondary drive wheels, respectively, so as to control a transmission torque. An example thereof is described in U.S. Pat. No. 8,313,407 B2. In the four-wheel-drive vehicle, by disengaging the connection-disconnection mechanism and the right and left clutches in a 2WD running state in which dynamic power is transmitted to only primary drive wheels for running, it is possible to stop rotation of rotation elements (such as the driving power transmission shaft) constituting a part of the power transmission paths between the connection-disconnection mechanism and the right and left clutches. In this case, it is possible to improve fuel efficiency compared with a case where only one of the connection-disconnection mechanism and the right and left clutches is disengaged in the 2WD running state.